Select correct statement

Options

A. If salt bridge is removed, potential falls to zero
B. KCl cannot be used as electrolyte in salt bridge in case of silver electrode
C. Cell reaction is spontaneous if emf is positive
D. All of these

Answer

To solve the question "Select correct statement," we will analyze each statement provided in the context of electrochemistry and determine their validity step by step.

### Step 1: Analyze the First Statement
**Statement:** If we remove the salt bridge, the potential will fall to zero.

**Explanation:** The salt bridge is essential in an electrochemical cell as it maintains electrical neutrality by allowing the flow of ions between the two half-cells. If the salt bridge is removed, the circuit becomes open, and no current can flow. Consequently, the potential difference (EMF) across the cell will drop to zero because the circuit is incomplete.

**Conclusion:** This statement is **true**.

### Step 2: Analyze the Second Statement
**Statement:** KCl cannot be used as an electrolyte in the salt bridge in case of silver electrode.

**Explanation:** In electrochemical cells involving silver (Ag) or lead (Pb), the salts formed (AgCl and PbCl2) are insoluble in water. If KCl is used in the salt bridge, it can lead to the precipitation of AgCl or PbCl2, which would interfere with the cell's operation. Therefore, KCl is not suitable for use in these cases.

**Conclusion:** This statement is **true**.

### Step 3: Analyze the Third Statement
**Statement:** A cell reaction is spontaneous if EMF is positive.

**Explanation:** The relationship between Gibbs free energy (ΔG) and the electromotive force (EMF, E) of a cell is given by the equation ΔG = -nFE, where n is the number of moles of electrons exchanged and F is Faraday's constant. If the EMF (E) is positive, ΔG will be negative, indicating that the reaction is spontaneous. Conversely, if the EMF is negative, the reaction is non-spontaneous.

**Conclusion:** This statement is **true**.

### Final Conclusion
After analyzing all three statements, we find that all of them are correct. Therefore, the answer to the question is:

**Answer:** All of these (Part D).

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